This invention relates to microencapsulated herbicidal compositions containing a haloacetanilide herbicide, and processes for preparation and for use of such compositions.
The haloacetanilides, particularly the subclass generally known as xcex1-chloroacetanilides, are a well-known class of herbicidal agents and have been used and proposed for use in a number of crop and non-crop applications. Some of the better known members of this class include xcex1-chloro-6xe2x80x2-ethyl-N-(2-methoxy-1-methylethyl)-acetanilide (metolachlor), N-butoxymethyl-xcex1-chloro-2xe2x80x2 ,6xe2x80x2-diethylacetanilide (butachlor), xcex1-chloro-2xe2x80x2 ,6xe2x80x2-diethyl-N-methoxymethylacetanilid e (alachlor), 2-chloro-N-(ethoxymethyl)-6xe2x80x2-ethyl-o-acetotoluidide (acetochlor) and xcex1-chloro-N-isopropylacetanildie (propachlor). Many other compounds of this type are disclosed in numerous patents.
Various patents and publications describe the production and application of microencapsulated formulations of haloacetanilide herbicides. These include U.S. Pat. Nos. 4,280,833; 4,417,916; 4,534,783; 4,563,212; and 4,640,709. Additionally, U.S. Pat. No. 4,936,901 discloses herbicidal compositions which are dry flowable water-dispersible granular formations comprising a mixture of microcapsules of a water-insoluble pesticide (including a haloacetanilide herbicide) encapsulated within a polymeric shell wall and at least one other pesticide which is nonencapsulated.
In the patents just mentioned, the microcapsule is formed in general with a shell wall of polyurea which is prepared in general from an aqueous phase material containing, for example, an emulsifier, and a water-immiscible phase consisting essentially of polymethylene polyphenylisocyanate and a water-immiscible herbicide, such as a haloacetanilide herbicide. To that is added, with agitation, a polyfunctional amine, which reacts with the polyphenylisocyanate to form a polyurea shell wall around the water-immiscible phase. This basic process is described in U.S. Pat. No 4,280,833. The remaining patents and patent application describe improvements in the process or microcapsules formed, such as specific emulsifiers which may be used in preparation of these microcapsules.
Microcapsule formulations are employed to achieve a slow or controlled release of the material encapsulated (in the present case, a water-immiscible haloacetanilide herbicide) into the surrounding or external medium. When properly done, the results are greater longevity of the encapsulated material and longer availability of it for its intended purpose. In the case of herbicides, microencapsulation provides a means for obtaining longer effective life of the herbicide in the surrounding medium, for instance in the soil, through a controlled released.
This benefit of increased longevity, however, can be offset by lack of sufficient activity of the material in the early period after application, and/or at relatively low application rates. Presumably this occurs because shortly after application, or at low rates, or both, there has been insufficient release of the active material (e.g. herbicide) to provide effective results, particularly in comparison with similar material applied in nonencapsulated form.
A typical comparison of the behavior of encapsulated as opposed to nonencapsulated forms of haloacetanilide herbicides is found in Example 17 of U.S. Pat. No. 4,280,833 (the same information is in Example 30 of U.S. Pat. No. 4,417,916). This example compares the performance of encapsulated and nonencapsulated (emulsifiable concentrate) forms of the haloacetanilide herbicide alachlor at varying concentrations and over a period of time. In the procedure of this example, alachlor is applied to weeds planted in aluminum pans at application rates ranging from 1.0 lb./acre down to 0.0078 lb./acre. As the example states, the results indicate that microencapsulated alachlor exhibited longer soil longevity than unencapsulated alachlor applied at the same rates. However, the same example also indicates that at the first rating period, two weeks after planting, the activity of encapsulated alachlor began to decrease at application rates below 0.5 lbs./acre on barnyardgrass and below 0.25 lbs./acre on crabgrass and green foxtail. Indeed, at an application rate of 0.0625 lbs./acre, the encapsulated alachlor was rated xe2x80x9c0xe2x80x9d on barnyardgrass and green foxtail, whereas the unencapsulated alachlor received ratings of 100 and 70, respectively.
Another process for production of microencapsulated forms of pesticides, including herbicides, is disclosed in U.S. Pat. No. 4,285,720. This process involves the preparation of microcapsules by a technique generally known as in situ interfacial condensation polymerization. In general, in the process described in U.S. Pat. No. 4,285,720, microencapsulated formulations containing pesticides are prepared by the steps of (a) providing, at room temperature, a dispersion of (i) a water-immiscible phase comprising a water-immiscible material (e.g., pesticide) to be encapsulated and an organic polyisocyanate in (ii) an aqueous phase comprising a solution of water, a surfactant and a protective colloid; and a (b) heating and maintaining said dispersion in a temperature range from about 40xc2x0 C. to about 90xc2x0 C.; where part of the water-immiscible material is encapsulated within discrete polyurea capsular enclosures.
U.S. Pat. No. 4,285,720 deals with the encapsulation of water-immiscible substances in general and contains examples showing encapsulation of water-immiscible organophosphorus insecticides, thiocarbamate herbicides, an insect hormone mimic, and an organophosphorus flame retardant. Another example shows the encapsulation of two water-immiscible substances by this process. Various products which can be encapsulated are discussed generally and specifically in columns 13 and 14. This patent does not, however, mention haloacetanilide herbicides as one type of substance which may be encapsulated by the process described.
Two other patents which describe modifications or improvements to the process described in U.S. Pat. No. 4,285,720 do include mention of haloacetanilide herbicides. U.S. Pat. No. 4,140,516 describes the use of a phase transfer catalyst in a process such as that described in U.S. Pat. No. 4,285,720, and mentions several haloacetanilide herbicides in column 12 to which the process may be applied. U.S. Pat. No. 4,448,929 describes an improved protective colloid for use in the process of U.S. Pat. No. 4,285,720 (among others) and mentions metolachlor and butachlor as two materials to which that modification may be applied.
It has now been found that use of the process as described in U.S. Pat. No. 4,285,720 can produce microencapsulated compositions of haloacetanilide herbicides which have the dual benefits of providing comparable herbicidal activity to nonencapsulated formulations of the same herbicide, even in the early stages of application and/or at lower application rates, while maintaining substantially lower mammalian toxicity compared with the nonencapsulated formulations.